The present invention generally relates to a method of making an article, particularly an abrasive article, comprising embedding heating particles into a polymeric sheet substrate using a flame or thermal sprayer.
There are many products which generally comprise a sheet of polymeric material with particulate material either within or on the surface of the sheet. For example, certain types of coated abrasive articles have abrasive particles bonded to a backing sheet using a polymeric binder.
Coated abrasive articles are conventionally produced by a multi-step coating process which typically involves applying a first polymeric binder or adhesive (known as a make coat) to a backing sheet or substrate; depositing abrasive particles on the make coat; drying and/or curing the make coat; and optionally, applying a second polymeric binder or adhesive (known as a size coating) to further aid the bond or adhesion of the abrasive particles to the sheet. Common coating processes are comparably slow principally because of long drying and/or curing times. In addition, such processes typically involve the use of organic solvents in the binders or adhesives, the removal and disposal of which must be carefully controlled to reduce the risk of pollution and damage to the environment.
As an alternative to the conventional coating process described above, U.S. Pat. No. 2,712,987 (Storrs et al.) reports a process of making an abrasive belt by softening a nylon substrate with a suitable solvent, and then distributing abrasive particles over the softened surface. The particles become embedded by gravity in the softened surface, after which any remaining solvent is evaporated and the nylon is hardened. U.S. Pat. No. 2,899,288 (Barclay) also reports a process for making an abrasive product in which a thermoplastic backing sheet is softened by heat and then abrasive particles are spread over the softened surface and pressed into the sheet by nip rollers. Further, U.S. Pat. No. 2,411,724 (Hill) reports a method for making an endless tubular abrasive element for a tool such as a rasp or file. A thermoplastic or thermosetting polymer is extruded to form a backing and, while the backing is hot, abrasive particles are blown into the backing which is then solidified. U.S. Pat. No. 3,813,231 (Gilbert et al.) reports a process where the abrasive particles are distributed over the surface of a polymeric film, which is then heated in a platen press to bond the particles to the film. U.S. Pat. No. 4,240,807 (Kronzer) reports a process where a paper substrate is coated with a heat-activatable binder which is softened by heat, and then abrasive particles are distributed over the binder and allowed to sink into the coated paper substrate. These reported processes, although generally free of solvents, are time and energy consuming and provide poor or inadequate adhesion of the abrasive particles to the polymeric backing. In an alternative process, U.S. patent application Ser. No. 08/583,990 (Sanders et al., filed Jan. 11, 1996) now U.S. Pat. No. 5,681,361 and PCT patent application Ser. No. US96/06276 (Beardsley et al., filed Jan. 15, 1996) report combining powdered resin and abrasive particles and then spray coating the mixture onto a lofty non-woven web.
Pavement marking materials and retroreflective articles, such as used on streets and in cross walks and on traffic signs use light reflective particles typically glass beads, bonded to or into a sheet of flexible and weather resistant sheet material. These types of articles have been made in many of the same processes as used to make abrasive articles except that light reflective particles are adhered to the substrate.
What is needed in the abrasives field, and other fields having similar constructions of attaching or fixing particles on a sheet product, is a method of producing the product quickly, economically, with minimal energy consumption, and without the use of solvents.